Measurement of blood pressure is the primary approach used to diagnose conditions such as hypertension. Conventionally, arterial pressures of the human circulatory system are measured through invasive means, for example, by penetrating the skin and taking pressure measurements from within the blood vessels, such as with intra-arterial techniques; or by non-invasive means, which provide an estimate of the actual pressure. The former approach is typically restricted to highly qualified and trained staff that monitor arterial lines on patients at intensive care centres within a hospital setting. The latter approach typically includes non-invasive techniques seen in general practice for routine examinations and monitoring. An exemplary arterial pressure waveform signal measured from an inter-arterial blood pressure monitor, including some of the associated features of the signal, is shown in FIG. 7.
As an example, two currently popular conventional approaches for conducting Non-Invasive Blood Pressure (NIBP) measurements both require direct physical contact to be established between an instrument and a human subject.
One of the conventional approaches, an auscultatory approach, uses a stethoscope and a sphygmomanometer. This approach includes an inflatable cuff placed around the upper arm at roughly the same vertical height as the heart, attached to a mercury or aneroid manometer.
The second of the conventional approaches, an oscillometric approach, is functionally similar to that of the auscultatory method, but with an electronic pressure sensor (transducer) fitted in the cuff to detect blood flow, instead of using the stethoscope and an expert's judgment. In practice, the pressure sensor is a calibrated electronic device with a numerical readout of blood pressure. To maintain accuracy, calibration must be checked periodically, unlike with the mercury manometer. In most cases, the cuff is inflated and released by an electrically operated pump and valve, which may be fitted on the wrist (elevated to heart height) or other area. The oscillometric method can vary widely in accuracy, and typically needs to be checked at specified intervals, and if necessary recalibrated.
Thus, conventional approaches require close access and direct physical contact with a human subject's body, typically with the arm of the subject. This contact requires that the subject is compliant and aware that a blood pressure measurement is underway. As an example, to acquire a subject's blood pressure, they must have knowledge of the measurement and be physically collocated with the NIBP instrument.